Poly(isobutylene-co-isoprene), or IIR, is a synthetic elastomer commonly known as butyl rubber which has been prepared since the 1940's through the random cationic copolymerization of isobutylene with small amounts of isoprene. As a result of its molecular structure, IIR possesses superior air impermeability, a high loss modulus, oxidative stability and extended fatigue resistance.
Butyl rubber is understood to be a copolymer of an isoolefin and one or more, preferably conjugated, multiolefins as co-monomers. Commercial butyl comprises a major portion of isoolefin and a minor amount, not more than 2.5 mol %, of a conjugated multiolefin. Butyl rubber or butyl polymer is generally prepared in a slurry process using methyl chloride as a diluent and a Friedel-Crafts catalyst as part of the polymerization initiator. This process is further described in U.S. Pat. No. 2,356,128 and Ullmann's Encyclopedia of Industrial Chemistry, volume A 23, 1993, pages 288-295.
Halogenation of this butyl rubber produces reactive allylic halide functionality within the elastomer. Conventional butyl rubber halogenation processes are described in, for example, Ullmann's Encyclopedia of Industrial Chemistry (Fifth, Completely Revised Edition, Volume A231 Editors Elvers, et al.) and/or “Rubber Technology” (Third Edition) by Maurice Morton, Chapter 10 (Van Nostrand Reinhold Company © 1987), particularly pp. 297-300. CA 2,418,884 and 2,458,741 describe the preparation of butyl-based, peroxide-curable compounds which have high multiolefin content. Specifically, CA 2,418,884 describes the continuous preparation of IIR with isoprene levels >4.1 mol %. Halogenation of this high multiolefin butyl rubber produces a reactive allylic halide functionality within the elastomer. With these elevated levels of isoprene now available, it is possible to generate BIIR analogues which contain allylic bromide functionalities ranging from greater than 3 mol %.
The presence of allylic halide functionalities allows for nucleophilic alkylation reactions. It has been recently shown that treatment of brominated butyl rubber (BIIR) with nitrogen and/or phosphorus based nucleophiles, in the solid state, leads to the generation of IIR-based ionomers with interesting physical and chemical properties (see: Parent, J. S.; Liskova, A.; Whitney, R. A; Resendes, R. Journal of Polymer Science, Part A: Polymer Chemistry 43, 5671-5679, 2005; Parent, J. S.; Liskova, A.; Resendes, R. Polymer 45, 8091-8096, 2004; Parent, J. S.; Penciu, A.; Guillen-Castellanos, S. A.; Liskova, A.; Whitney, R. A. Macromolecules 37, 7477-7483, 2004). The ionomer functionality is generated from the reaction of a nitrogen or phosphorous based nucleophile and the allylic halide sites in the BIIR to produce an ammonium or phosphonium ionic group respectively. The physical properties of these BIIR based ionomers (green strength, modulus, filler interactions etc.) are superior to those of their non-ionomeric counterpart.
It has been previously discovered that the addition of para-methylstyrene to the mixed feed of butyl polymerizations (MeCl, IB and IP mixed feed, with AlCl3/H2O as initiator) results in a high molecular weight polymer with up to 10 mol % of styrenic groups randomly incorporated along the polymer chain (Kaszas, U.S. Pat. No. 6,960,632; Kaszas et al. Rubber Chemistry and Technology, 2001, 75, 155). The incorporation of para-methylstyrene is found to be uniform throughout the molecular weight distribution due to the similarity in reactivity with isobutylene. The isoprene moieties within the butyl terpolymers can be halogenated by conventional methods.
A copolymer may be formed comprising a C4-C7 isomonoolefin, such as isobutylene, and a comonomer, such as para-alkylstyrene, preferably para-methylstrene, wherein some of the alkyl substituent groups present in the styrene monomer units contain a benzylic halogen or other functionality copolymer. Additional functional groups can be incorporated by nucleophilic displacement of the benzylic halogen with a variety of nucleophiles as described in U.S. Pat. No. 5,162,445. Use of tertiary amines and phosphines results in the formation of ionomers with improved physical properties from these copolymers.
The preparation and use of butyl latex has been reported previously (see for example U.S. Pat. Nos. 2,944,038, 3,005,804, 3,983,062, 7,119,138, WO 2006/115729, WO 2005/063871, WO 2005/061608). However, one of the biggest factors in the preparation of these latexes is the ease of making the latex and the final stability of the latex. The stability of the latex is commonly achieved by the use of surfactants. While surfactants act as stabilizers during production, they typically have a detrimental effect on the properties of a dry latex film, for example, due to their tendency to migrate and adversely affect the end use properties of the material (i.e. adhesion, resistance to the growth of microbes). Surfactants may also cause the unwanted blooming that leads to surface irregularities in the resulting latex that is applied to a substrate. Once a latex film is formed surfactants will leach or be extracted when in contact with aqueous solutions. It would therefore be desirable to reduce or eliminate the need for surfactants in forming a butyl latex.
U.S. Pat. No. 7,238,736 describes the improved filler dispersion observed when using butyl ionomers as compared to regular butyl resulting in articles with improved tensile strength. It would be desirable to provide improved filler dispersion in a butyl latex.
U.S. Pat. No. 7,915,333 describes compositions where improved barrier properties are observed with butyl ionomers and nanocomposites while maintaining tensile properties. It would be desirable to provide improved barrier properties in a butyl latex.
WO2010/091499 describes butyl ionomer compositions having anti-microbial and anti-bacterial properties. It would be desirable to provide improved anti-microbial properties in a butyl latex.
U.S. Pat. No. 7,662,480 describes improved adhesion of butyl ionomers to a substrate as compared to a non-ionomeric butyl rubber. It would be desirable to provide improved coating adhesion in a butyl latex.
There is therefore a need for improved butyl latexes, preferably exhibiting some or all of the above desirable properties.